1. Field of the Invention
The present invention relates to conductive polymers, and more particularly to composite articles incorporating ion-conductive polymers.
2. Description of the Related Art
In recent years there has been an increased demand placed on materials manufacturers and suppliers to develop relatively non-corrosive, strong, and lightweight materials for use as structural members and panels. For instance, in the transportation industry, emphasis has been placed on the use of materials such as plastics, and plastic-matrix composites, in applications requiring reduced vehicle weight and improved corrosion resistance.
As compared with many metals, however, plastic materials suffer some disadvantages. One such disadvantage is the difficulties encountered when coating plastic articles for decorative or functional purposes. In general, it is difficult to achieve relatively good adhesion of many coatings to plastic articles. Relatively high quality surface finishes on coated plastic surfaces are also difficult to obtain using many ordinary coating compositions and methods.
Electrostatic coating compositions and methods have been proposed as a solution to the surface adhesion and finish problems of many coated materials. Unfortunately, electrostatic coating methods, such as those disclosed in the McGraw-Hill Encyclopedia of Science & Technology, Vol. 6, pp. 250-252 (6th ed. 1987) (hereby expressly incorporated by reference) tend to be useful in a limited number of practical applications. For instance, many plastic materials are undesirable candidates for employment with electrostatic coating compositions and methods.
Another disadvantage of many plastic materials is that, in general, plastic materials are undesirable for protecting underlying articles from some of the consequences of natural phenomena, such as being struck by lightning, or excessive amounts of electromagnetic interference. That is, the generally non-conductive nature of many plastics tends to inhibit the desired disbursement of charge (such as from a lighting bolt) over a surface. Such disbursement of charge is important to protect underlying articles from the direct and indirect effects of an excessive charge buildup. The use of metal foils for lightning protection and electric shielding of composite aircraft structures is suggested in "Materials in Action", Advanced Materials and Processes, p. 24 (May, 1989).
It has been suggested that electron-conductive polymers be employed to make articles somewhat conductive. Two presently popular types of electron-conductive polymers that have potential for some commercial applications are polyheterocyclic cations and polyacetylenes. Polyheterocyclic cations, e.g., polypyrrole, are generally resistant to oxidation and have relatively moderate electrical conductivities. However, such materials generally have poor mechanical and processing properties. Polyacetylenes, in turn, have relatively high electrical conductivities when doped, but tend to have relatively poor stability in air. Recently, conductive polymers have received increased attention in the literature as exemplified by the following references, which are hereby expressly incorporated by reference.
"Materials for the New Batteries", by J. W. Braithwaite, Advanced Materials and Processes, Apr. 1987, pp. 67-73 discloses polymer electrolytes for use in batteries.
"Polymers: Exotic Composite Materials", by H. H. S. Javadi, Microwave Journal (Feb., 1989) pp. 162-164 discloses polyaniline conducting polymers that are doped (protonated) to impart conductivity, and are particularly useful for microwave attenuators and terminations.
"Highly Electroconductive Polypyrrole Composites", by V. Bocchi, G. Gardini, and S. Rapi, J. Materials Science Letters 6 (1987) 1283-1284 discloses ferrite salt additions to polypyrrole to improve conductivity.
"Polymers and Composites that Conduct Electricity", by A. J. Klein, Advanced Materials & Processes, Jan. 1986, pp. 28-33 discloses the addition of dopants, fillers or special heat treatments to impart electrical conductivity to a polymer.
"Conductive Composites Past, Present, and Future", by R. Crossman, Polymer Engineering and Science, Mid-June, 1985, Vol. 25, No. 8, pp. 507-513, discloses conductive plastics and polymer composites.
"Solid Ionic Conductors", by D. F. Shriver and G. C. Farrington, C&EN, May 20, 1985, pp. 42-57 discloses polymeric solid electrolytes and applications therefore such as for use as electroytes in solid-state batteries.
"Polyethers as Solid Electrolytes", by M. B. Armand, J. M. Chabagno, M. J. Duclot, in Fast Ion Transport in Solids, Electrodes and Electrolytes Proceedings International Conference, edited by P. Vashishta, J. N. Mundy, and G. K. Shenoy, eds., pp. 131-136 (1979), discloses the effect of temperature on polyethers as solid electrolytes as well as on poly (ethylene oxides) and poly (propylene oxides) as adducts with selected alkali metal salts.
"Lithium Ion Conducting Polymeric Hybrids", by E. Isuchida and K. Shigehara, Mol. Cryst. Liq. Cryst., 1984, Vol. 106, pp. 361-369 discloses preparation of plastic solid electroytes from inorganic lithium salts and polymer matrices.
"Ionic Conductivity and Mobility in Network Polymers from Poly (Propylene Oxide) Containing Lithium Perchlorate", by M. Watanabe, K. Sanui, N. Ogata, T. Kobayashi, and Z. Ohtaki, J. Appl. Phys. 57(1), Jan. 1 1985, pp. 123-128 discloses ionic conductivity and mobility in amorphous network polymers from poly (propylene oxide) containing lithium perchlorate.
"Lithium Fast-Ion Conductors: Polymer-Based Materials", by J. Wasson, Office of Naval Research, Contract N00014-83-C-0440, Final Report, May 30, 1987 discloses lithium-containing materials (particularly polymers) exhibiting improved ambient temperature ionic conductivities. Metal salt doped polymers including poly (ethylene oxide) and poly (vinyl acetate) and poly acrylonitride are also discussed.
"Synthesis of Ionic Conducting Interpenetrating Polymer Networks", by C. K. Chiang, B. J. Bauer, R. M. Briber, and G. T. Palls, Office of Naval Research, Contract N00014-86-70020, Task No. 14339, Technical Report No. 5, Aug. 14, 1986 discloses epoxy and ion conducting poly (ethylene oxide)-salt complexes for interpenetrating polymer networks. The epoxy discussed forms a phase with good mechanical properties, while the ionic polymer provides for conductivity.
"Materials Pace Aerospace Technology", by J. J. DeLuccia, R. E. Trabocco, J. Waldman, and J. F. Collins, Advanced Materials & Processes, pp. 39-50 (May, 1989) discloses the use of conductive polymers in applications such as control devices or batteries.
"Directions in Automotive Materials", by Jack Simon, Advanced Materials and Processes, Inc., Metal Progress, Jan. 1988, pp. 63-65, discloses in-mold coating of sheet molding compound body panels with conductive (filled) thermoset polyester coatings.
U.S. Pat. No. 4,532,169 issued Jul. 30, 1985 (Carley) discloses molding an electrically conductive surface into a composite material to enchance electrostatic paintability of plastic parts (see e.g., Column 2).
All percentages herein refer to weight percent unless otherwise indicated.